internal void OnCollectionChanged(IReadOnlyCollection <string> oldItems, IReadOnlyCollection <string> newItems)
 {
     if (oldItems.SequenceEqual(newItems))
     {
         return;
     }
     collectionChangedEvent.Fire(oldItems, newItems);
 }
 void OnCollectionChanged(IReadOnlyCollection <string> oldItems, IReadOnlyCollection <string> newItems)
 {
     this.listSnapshot = list.ToArray();
     collectionChangedEvent.Fire(oldItems, newItems);
 }